1. Field of the Invention
This invention relates in general to the construction of pipe-forming devices and, in particular, to a new and useful apparatus for forming pipe from sheet metal including both a preforming die and punch and a finishing tool, including a punch with separately pivotable mandrel parts.
2. Description of the Prior Art
In the known tooling arrangements for making pipe bends by cold shaping a piece of sheet metal, a preforming tool with a preforming die and a drawing punch are used for shaping the back of the bend. The preforming die has a cross-sectional shape which includes two spaced parallel surfaces between which there is a semicircle corresponding to the back formation of the pipe bend to be formed. Therefore, when the drawing punch descends, the longitudinal side parts of the sheet project out of the side into the open. A finishing tool includes a reforming die which is used as the holding die. A two-part mandrel is inserted by hand into the preformed sheet and a punch is moved to seize the longitudinal side parts of the sheet which project out of the preforming die and which is used as a holding die in the finishing operation. The sheet is bent around the mandrel in order to form the pipe bend. After the mandrel is removed, the edges of the longitudinal side parts of the sheet which run along the inside of the bend are joined together by a continuous weld. With such a known tooling arrangement, only bends with relatively thick walls in relation to the diameter can be satisfactorily made because, as the wall thickness decreases, the sheet tends to form folds when being operated on both by the preforming and the finishing tools. These folds cannot be removed even during the complete closing of the preforming which occurs by action of the finishing tools. In addition, the awkward manipulation which is involved in the known tooling arrangement is troublesome, particularly in respect to the use of the mandrel which is required by the finishing tools.